$primaryColor: #00a0e9;
//写个弹性盒子
@mixin flexbox($dir: row, $j: flex-start, $a: stretch) {
  display: flex;
  //弹性方向
  flex-direction: $dir;

  justify-content: $j;

  align-items: $a;
  @content; //占位符
}

// flexbox()
